In FIG. 9, an example of a CT scanning device 100 as one type of medical equipment is illustrated. The CT scanning device 100 is configured to diagnose and analyze a pathological symptom through irradiation with an X-ray or the like. The CT scanning device 100 includes an examination unit 101 having an opening 101A, and a bed unit 102 movable in the opening 101A of the examination unit 101 with an object 110 to be examined, for example, a human body, lying thereon. The examination unit 101 includes a ring-shaped rotator 105 (gantry) having an X-ray irradiation device 103 and a detection unit 104 arranged so as to be opposed to each other in a diameter direction. The rotator 105 is rotatably supported by a cylindrical stationary unit 106 through intermediation of a bearing 1.
The CT scanning device 100 is configured to rotate the rotator 105 about the bed unit 102 while irradiating the object 110 to be examined with an X-ray from the X-ray irradiation device 103 so as to detect the X-ray having passed through the object 110 to be examined with the detection unit 104, thereby obtaining a tomographic image of the object 110 to be examined.
In the CT scanning device 100, in order to form the opening 101A of the examination unit 101 into such a dimension that the object 110 to be examined may pass through the opening 101A (diameter of about 1 m), and to downsize the CT scanning device 100 itself, it is necessary to reduce a space of a rotation support unit 107 on which the bearing 1 is arranged. Therefore, a so-called ultrathin double-row angular contact ball bearing having a significantly small ball diameter with respect to a pitch circle diameter of balls is used as the bearing 1. The ultrathin double-row angular contact ball bearing refers to an ultrathin double-row angular contact ball bearing having an inner diameter of 650 mm or more and having a value of a ratio Db/PCD of a diameter Db of each of rolling elements to a pitch circle diameter PCD of the rolling elements of 0.03 or less.
In Patent Document 1, there is described a double-row angular contact ball bearing for a CT scanning device, including an inner member made up of a pair of raceway rings. Positioning holes are formed through the pair of raceway rings, and a positioning member is inserted into the positioning holes so as to suppress radial decentering of the pair of raceway rings. Both the raceway rings are fastened by a plurality of fixing bolts. The double-row angular contact ball bearing for a CT scanning device does not use a related-art spigot structure between the pair of raceway rings and suppresses the decentering of the pair of raceway rings by the positioning member inserted into the positioning holes, and is easy to manufacture and enables a cost reduction.